For high production volume electronic devices it is important that quality control be properly monitored. This is so regardless of whether the device being tested presents a complex load or a sensitive load. For purposes of the present invention, a complex load is one having a multitude of major current carrying terminals that must be at different voltages. On the other hand, a sensitive load is one that is easily subject to unwanted damage or undesirable changes due to slight deviations in voltage, current, power, heating, frequency, or any other applied electrical quantity other than specified.
The importance of test monitoring is at least two-fold. First, it is necessary to know that the product actually works as intended and, secondly, it is necessary to know that it will work reliably for an extended period of time. It is, of course, quite impractical to subject a product to a simulated operational environment for the entire life expectancy of the product. In some instances this could require years. In fact, the life expectancy of the product may not even be known, and may itself be an objective of the testing. Consequently, accelerated or destructive testing is done to determine long term reliability of the product within a relatively short period of time. As implied above, this testing must be done reliably, predictably and precisely.
Semiconductor testing provides an example where the long term electromigration and oxide breakdown characteristics of an electronic device, the semiconductor, can be tested in a relatively short period of time. Typically, this testing is done by applying a substantially constant current through the device. To accomplish this, the input current to the device is monitored and is appropriately adjusted to maintain the current at a substantially constant value. Unfortunately, testing equipment which uses such a scheme can sometimes prematurely destroy the device being tested, before it can be effectively tested. Primarily such destruction is caused by current surges through the device which result from erratic interruptions in the test circuitry. Not surprisingly, tests can sometimes require relatively high current levels. If so, the damage can be extensive.
Environmental conditions during a test, such as unwanted vibrations on either the test equipment or the device being tested, can cause erratic interruptions. When such an interruption occurs, the current through the device being tested will diminish or be entirely cut off. In response, the voltage which is being applied to maintain a substantially constant current through the device being tested will increase dramatically. A reconnection of the circuitry after the interruption then results in a current surge and possible destruction of the device. The test results are consequently unusable. Unfortunately, all of this can happen before any software which is being used to monitor the test circuitry can establish proper control. Further, as will be appreciated by the skilled artisan, voltage and current fluctuations can also cause damage to the test apparatus itself.
In light of the above, it is an object of the present invention to provide an apparatus for testing an electrical device which obviates current surges through the device by controlling the voltage input to the device. Another object of the present invention is to provide an apparatus for testing an electrical device which is capable of applying a regimen of carefully controlled and monitored electric power to either a complex load or a sensitive load. Another object of the present invention is to provide an apparatus for testing an electrical device which has the flexibility to conduct various test procedures or protocols on the device, to include tests using relatively high current levels. Yet another object of the present invention is to provide an apparatus for testing an electrical device which prevents damage to the test apparatus itself. Still another object of the present invention is to provide an apparatus for testing an electrical device which is relatively simple to manufacture, is functionally easy to use, and is comparatively cost effective.